Segmented thermoplastic copolyesters modified with polyepoxides

ABSTRACT

A thermoplastic copolyester composition comprising: (a) at least one segmented copolyester polymer consisting essentially of (1) about 5-85 weight percent of recurring long-chain ester units derived from at least one dicarboxylic acid having a molecular weight below about 300 and at least one poly(alkylene oxide) glycol having a molecular weight between about 400-6,000 and a carbon to oxygen ratio of about 2.0-4.3 and (2) 15-95 weight percent short-chain ester units which are derived from at least one low molecular weight diol having a molecular weight of less than about 250 and at least one dicarboxylic acid having a molecular weight of less than about 300, and (b) from 0.5-10 equivalents, per equivalent of carboxyl group contained in said copolyester of a polyepoxide having a functionality of not less than about 2.

United States Patent 91 Hoeschele [4 Mar. 27, 1973 A 22 Filed:

[75] Inventor: Guenther Kurt Hoeschele, Wilmington, Del.

[73] Assignee: E. 1. du Pont de Nemours and Company, Wilmington, Del.

Feb. 28', 1972 [21] Appl. No.: 230,045

52 US. Cl. ..260/835, 260/40 R, 260/459 R, 260/47 R, 260/75 R, 260/830 R, 260/860 51 1 1m. Cl. ..C08g 45/14 58 Field of Search ..260/830 R, 835

[56] References Cited UNITED STATES PATENTS 2,890,196 6/1959 Phillips ..260/835 2,890,197 6/1959 Phillips 260/835 2,935,488 5/1960 Phillips... 260/835 3,297,782 l/l967 Barkis 260/835 3,378,497 4/1968 260/830 R 3,397,254 8/1968 Wynstra ..260/835 3,670,045 6/ 1972 Koleske ..260/830 R FOREIGN PATENTS 0R APPLICATIONS 872,254 7/1961 Great Britain .260/835 Primary Examiner-Paul Lieberman Attorney-Michael Conner [5 7] ABSTRACT A thermoplastic copolyester composition comprising: (a) at least one segmented copolyester polymer consisting essentially of (1) about 5-85 weight percent of recurring long-chain ester units derived from at least one dicarboxylic acid having a molecular weight below about 300 and at least one poly(alkylene oxide) glycol having a molecular weight between about 400-6,000 and a carbon to oxygen ratio of about 2.0-4.3 and (2) l595 weight percent short-chain ester units which are derived from at least one low molecular weight diol having a molecular weight of less than about 250 and at least one dicarboxylic acid having a molecular weight of less than about 300, and (b) from 05-10 equivalents, per equivalent of carboxyl group contained in said copolyester of a polyepoxide having a functionality of not less than about 2.

16 Claims, No Drawings SEGMENTED THERMOPLASTIC COPOLYESTERS MODIFIED WITH POLYEPOXIDES BACKGROUND OF THE INVENTION Linear copolyesters or copolyetheresters have been produced heretofore for various purposes, particularly certain polymers of this type which possess very desira- 1 ble properties such as superior tear strength, tensile strength, flex life and abrasion resistance may, for particular designated uses, have to be improved with regard to a characteristic such as meltstability. Melt stability may be defined as resistance toward polymer degradation during processing in the molten state. Improved melt stability is required when processing temperatures are raised significantly above polymer melt temperature and/or when processing requires that the polymer be held above its melting point for extended periods of time. In filling large molds by injection molding or rotational casting, high processing temperatures (up to 3050C. above normally recommended temperatures) are needed to lower polymer melt viscosity.

Under these conditions, conventional copolyetherester polymers degrade at a relatively high rate. The degradation is evidenced by lower inherent viscosity and higher melt index and results in a reduction of polymer physical properties such as tear and tensile strengths as well as flex life. Thus, for uses such as molding a large object, e.g., an airplane tire, superior melt stability is a necessity.

In addition, there are instances where it is desirable to increase the molecular weight of a copolyetherester to improve its physical properties. While it is generally possible to prepare copolyetheresters of high molecular weight by known procedures, expensive continuous polycondensation equipment capable of handling high viscosity polymer melts is required and the output of such equipment is limited. By producing intermediate molecular weight polymer, less expensive equipment such as batchxreactors can be used and/or output can be increased. The low melt viscosity of intermediate molecular weight polymers can also be an advantage in processing on occasion but means for eventually increasing the molecular weight of the polymer must be available. 7

SUMMARY OF THE INVENTION According to this invention there is provided an improved thermoplastic copolyester polymer which possesses superior melt stability; optionally, the molecular weightof the polymer can be increased. A process for making such a thermoplastic elastomer is also intended to be part of this invention. In order to produce such an improved thermoplastic copolyester composition a polyepoxide having a functionality of not less than two must be included in the polymer.

The thermoplastic copolyester which is to be improved by the instant invention consists essentially of a multiplicity of recurring intralinear long-chain and short-chain ester units connected head-to-tail through ester linkages, said long-chain ester units being represented by the following structure:

0 wherein:

and said short-chain ester units being represented by the following structure: I

G is a divalent radical remaining after removal of terminal hydroxyl groups from poly(alkylne oxide) glycols having a carbon-to-oxygen ratio of about 2.0-4.3 and molecular weight between about 400 and 6,000;

R is a divalent radical remaining after removal of car boxyl groups from a dicarboxylic acid having a molecular weight less than about 300', and

D is a divalent radical remaining after removal of hydroxyl groups from a low molecular weight diol hav ing a molecular weight less than about 250,

with the provisos that the short-chain ester units con= stitute about 15-95 percent by weight of the copolyester and, ergo, the long-chain ester units con stitute about 5 to percent by weight of the copolyester; at least about 50 percent of the shortchain ester units must be identical and a homopolymer in the fiber-forming molecular weight range 5,000) consisting of the identical short-chain ester units must melt at, at least, C.

The copolyester is modified by adding to it, after it is formed about 0.5-l 0 equivalents per equivalent of carboxyl group contained in the copolyester of a polyepoxide having a functionality of not less than about two.

The polyepoxide used has an epoxide equivalent of about 50-2,000 and may be depicted by the general fonnula:

where n has a value of about 2 to 15, R, R' and R"" are independently hydrogen or lower alkyl, e.g., C to C and R" is a polyvalent radical containing onlythe elements of C, H and O with the exception that carbocyclic aromatic nuclei contained in R" may be substituted with Cl or Br. R and R" may also be joined to form a 5 or 6 membered carbocyclic ring.

In an embodiment of the instant invention an epoxy catalyst may also be added to the copolyester.

. DETAILED DESCRIPTION The term long-chain ester units as applied to units in a polymer chain refers to the reaction product'ofa long-chain glycol with a dicarboxylic acid. Such longchain ester units, which are a repeating unit in the copolyesters of this invention, correspond to formula (a) above. The long-chain glycols are polymeric glycols having terminal (or as nearly terminal as possible) hydroxy groups and a molecular weight from about methane,

400-6,000. The long-chain glycols used to prepare the copolyesters of this invention are poly(alkylene oxide) glycols having a carbon-to-oxygen ratio of about 2.0-4.3.

Representative long-chain glycols are poly(ethylene oxide) glycol, poly(l,2- and 1,3-propylene oxide) glycol, poly-(tetramethylene oxide) glycol, random or block copolyrners of ethylene oxide and 1,2-propylene oxide, and random or block copolymers of tetrahydrofuran with minor amounts of a second monomer such as S-methyltetrahydrofuran (used in proportions such that the carbon-to-oxygen mole ratio in the glycol does not exceed about 4.3).

The term short-chain ester units as applied to units in a polymer chain refers to low molecular weight compounds or polymer chain units having molecular weights less than about 550. They are made by reacting a low molecular weight diol (below about 250) with a dicarboxylic acid to form ester units represented by formula (b) above.

included among the low molecular weight diols which react to form short-chain ester units are acyclic, alicyclic, and aromatic dihydroxy compounds. Preferred are diols with 2-15 carbon atoms such as ethylene, propylene, tetramethylene, pentamethylene, 2,2,dimethyltrimethylene, hexamethylene, and decamethylene glycols, dihydroxy cyclohexane, cyclohexane dimethanol, resorcinol, hydroquinone, 1,5-dihydroxy naphthalene, etc. Especially preferred are aliphatic diols containing 2-8 carbon atoms. Ineluded among the bis-phenols which can be used are bis(p-hydroxy) diphenyl, bis(p-hydroxyphenyl) I and bis(p-hydroxyphenyl) propane. Equivalent ester-forming derivatives of diols are also useful (e.g., ethylene oxide or ethylene carbonate can be used in place of ethylene glycol). The term low molecular weight diols" as used herein should be construed to include such equivalent ester-forming derivatives;.provided, however, that the molecular weight requirement' pertains to the diol only and not to its derivatives.

Dicarboxylic acids which are reacted with the foregoing long-chain glycols and low molecular weight diols to produce the copolyesters of this invention are aliphatic, cycloaliphatic, or aromatic dicarboxylic acids of a. low molecular weight, i.e., having a molecular weight of less than about 300. The term dicarboxylic acids as used herein, includes equivalents of dicarboxylic acids having two functional carboxyl groups which perform substantially like dicarboxylic acids in reaction 1 with glycols and diols in forming copolyester polymers. These equivalents include esters and ester-forming derivatives, such as acid halides and anhydrides. The molecular weight requirement pertains to the acid and not to its equivalent ester or ester-forming derivative. Thus, an ester of a dicarboxylic acid having a molecular weight greater than 300 or an acid equivalent of a dicarboxylic acid having a molecular weight. greater than 300 are included provided the acid has a molecular weight below about 300. The dicarboxylic acids can contain any substituent groups or combinations which do not substantially interfere with the copolyester Aromatic dicarboxylic acids, as the term is used 0 herein, are dicarboxylic acids having two car-boxy! groups attached to a carbon atom in an isolated or fused benzene ring. It is not necessary that both functional carboxyl groups be attached to the same aromatic ring and where more than one-ring is present, they can be joined by aliphatic or aromatic divalent radicals or divalent radicals such as -0 or SO,.

Representative aliphatic and cycloaliphatic acids which can be used for this invention are sebacic acid, 1,3-cyclohexane dicarboxylic acid, 1,4-cyclohexane dicarboxylic acid, adipic acid, glutaric acid, succinic acid, carbonic acid,'oxalic acid, azelaic acid, diethylmalonic acid, allylmalonic acid, 4-cyclohexene-l ,2- dicarboxylic acid, 2-ethylsuberic acid, 2,2,3,3 tetramethylsuccinic acid, cyclopentanedicarboxylic acid, decahydro-l,S-naphthalene dicarboxylic acid, 4,4'-bicyclohexyl dicarboxylic acid, decahydro-2,6- naphthalene dicarboxylic acid, 4,4'-methylenebis- (cyclohexane carboxylic acid), 3,4-furan dicarboxylic acid, and l,l-cyclobutane dicarboxylic acid. Preferred aliphatic acids are cyclohexane-dicarboxylic acids and adipic acid.

Representative aromatic dicarboxylic acids which can be used include terephthalic, phthalic andphenanthrene dicarboxylic acid, anthracene dicarboxylic acid, '4,4'-sulfonyl dibenzoic acid, and C -C alkyl and ring substitution derivatives thereof, such as'halo, alkoxy, and aryl derivatives. Hydroxyl acids such as p(fl-hydroxyethoxy) benzoic acid can also be used providing an aromatic dicarboxylic acid is also present.

Aromatic dicarboxylic acids are an especially preferred class for preparing the copolyetherester polymers of this invention. Among the aromatic acids, thosewith 8l6 carbon atoms are preferred, particularly the phenylene dicarboxylic acids, i.e., phthalic, terephthalic and isophthalic acids and their dimethyl derivatives.

It is essential that at least about 50 percent of the short segments are identical and that the identical segments form a homopolymer in the fiber-forming molecular weight range (molecular weight 5,000) having a melting point of at least C. and preferably greater than 200C. Polymers meeting these requirements exhibit a useful level of properties such as tensile strength and tear strength. Polymer melting points are two may be utilized for modifying the copolyester of -by epoxidation of olefins or by reaction of conveniently determined by differential scanning H calorimetry. c 1-oHgo The short-chain ester units will constitute about l5-95 weight percent of the copolyesters. The remainder of the copolyester will be the .long segments, ergo the long segment will comprise about 5-85 weight percent of the copolyester.

The carboxyl group content of the polymer is a maxclude those prepared by reaction of epichlorohydrin imum of I00 milliequivalent per kilogram, and is m with polyhydrie phenols such as 4,4-isopropylidene preferably about -75 milliequivalents per kilogram.

The copolyester is modified by the presence of a i l, polyepoxide having at least two functional groups; opm th l n bi h l) d l henols de i d from tionally, in an embodiment of the instant invention an phenol or o-cresol and an aldehyde (novolacs). Other epoxy catalyst may be added to the modified 15 suitable polyepoxides include reaction products of copolyester to increase the rate of reaction of the epichlorohydrin and aliphatic compounds containing 2 epoxy groups with the carboxyl groups of the copolyester. The addition of catalyst is particularly butanediol-l,4,poly(alkylene oxide) glycols and triols, beneficial in those instances where it is desired to inglycerol, l,2,6-hexanetriol, pentaerythritol and sorcrease the molecular weight of a polyester significantly bitol. Polyglycidyl esters of polycarboxylic acids such through chain-extension or cross-linking.

.The polyepoxide having a functionality of at least two is added to the copolyester in the amount of 0.5-10 epoxy equivalents for each equivalent of carboxyl group contained in the copolyester preferably 1.0-5.0 equivalents for each equivalent of carboxyl group and where n is 2-10 and R" has the meaning given herein hydroquinone, pyrogallol 4,4 F

acid are also representative of suitable polyepoxides.

Certain individual polyepoxides having at least two functionalities are particularly preferred in the instant invention. They include diglycidyl ethers of bisphenol A having the following structure:

o em ea 7 em e o cm-oH-cm O-Q-G-Q-OCm-CH-Cm o--e -oomocm (3H3 CH;

most preferably 1.5 to 4.0 equivalents f6? each wiii is to zero to Sand thejpolyglycidylet hers 6r equivalent of carboxyl group. I

Any polyepoxide having a functionality of at least structure:

of CH2CHCII2O portion-CH1 I where IS l to 5. I the instantjnyqntiom It is prefg 'ed however to use The polyepoxide is added (0 thecopolyester by polyepoxides having the following general formula:

such as rubber mills, extruders and internal mixers (Banbury mixer). I

where n 2-10 and R and R have the meanings given hereinbefore and the polyepoxide has an epoxide equivalent of 75-l,000. Epoxide compounds obtained epihalohydrins with active hydrogen compounds are useful in the present compositions.

Representative p y p obtained y p N-methylcyclohexylamine, N-methylpiperazine, include Vinyleyelohexene dioxide, P y' piperidine, pyrrolidine and 4,4'-dipiperidine; tertiary. y p y ether, p y y y y i aliphatic amines such as N,N-dimethylbenzylamine,- epoxycyclohexane carboxylate, bis(3,4-epoxy-6- N,N.di m 1 l h l i methylcyclohexylmthyl) adipate, p ypiperazine, N-ethylmorpholine, N-methylpiperidine y P y- P L land triethylene diamine; metallic salts of organic acids epoxidized butadiene and epoxidized natural oils. h as l i steal-ate, i hth t di m Epoxides prepared from epiholohydrins and active Suitable epoxy catalysts which may be utilized'inare preferred for use in the present compositions. boron trifluoride, zinc chloride, stannic chloride, boron These polyepoxides maybe represented by the general trifluoride-piperidine-complex and boron trifluorideformula: monoethanolamine complex.

before and the polyepoxide has an epoxide equivalent of -750. Representative polyepoxides of this type in-- diphenol (bisphenol A), tetrabromobisphenol A, resorto 6 alcoholic hydroxyl groups such as ethylene glycol,

as adipic acid, succinic acid, phthalic acid and mellitic phenolformalclehyde novolacs having the following ostrich-ion:

ing at elevated temperatures near the softening point or melting point of the copolyetherester in equipment elude secondary aliphatic amines such as dibutylamine.

N,N'-dimethylv acetate, stannous octoate and lead naphthenate; and hydrogen compounds; that is, polyglycidyl compounds;l metal halide Lewis acids and their complexes such as Of these catalysts, the secondary aliphatic amines are preferred and higher boiling secondary amines having boiling points approaching or exceeding the melting point of the copolyester are especially preferred because they are largely retained during mixing with the copolyetheresters. 4,4 '-Trimethylenedipiperidine has been found to be especially effective and convenient to use in the present compositions.

The presence arias epoxy eaiaigsrserves toincreas e the rate of chain-extension and/or cross-linking which is believed to result from reaction of epoxide groups with carboxyl groupspresent in the copolyester. In the absence of a catalyst, the copolyester and the polyepoxide interact at temperatures above the melting point of the copolyester at rates which in general approach or about match the rate of degradation of the copolyester. As a result, the melt index of the copolyester with the polyepoxide increases slowly or remains about unchanged with time. In the presence of a catalyst, the rate of reaction of the epoxide with the molten copolyestercan be increased significantly relative to the rate of copolyester degradation, with the result that themeltindex decreases as a function of time. Variables such as the carboxyl content of .the copolyester, the melt stability of the copolyester, the functionality and reactivity of the epoxide compound and catalyst concentration effect the results obtained in a manner consistent with the reactions which are believedto occur in-the epoxide/copolyester compositions.

ecause the interaction of polyepoxide and the copolyester is relatively slow, it is possible to melt blend the polyepoxide and copolyester, even in the presenceof a catalyst, and to form the blend into finished articles by molding or extrustion for instance and further cure (chain-extend and/or cross-link), the resulting articles at temperatures of l00l 50C. When epoxides having a higher functionality are used, curing, can result in the formation of highly cross-linked copolyesters which are thermosetting and have outstandingly high modulus characteristics for a given hardness.

'MBYfiffid' segmented copolyester; for use in this invention are those prepared from dimethyl terephthalate, 1,4-butanediol, and poly(tetramethylene oxide) glycol having a molecular weight of about GOO-2,000 or poly(ethylene oxide) glycol having a molecular weight of about 600-l,500. Optionally, up. to about mole percent and preferably 5-20 mole percent of the. dimethyl terephthalate in these polymers: can be replaced by dimethyl phthalate or dimethyl; isophthalate. Other preferred copolyesters are those prepared from dimethyl terephthalate, 1,4-butanediol, and poly(propylene oxide) glycol having a molecular weight of about 600-1 ,600. Up to 30 mole percent and preferably 10-25 mole percent of the dimethylv terephthalate can be replaced with dimethyl isophthalate or butanediol can be replaced with neopentyl glycol until up to about 30 percent and preferably 10-25 percent of the short-chain ester units are derived from neopentyl glycol in these poly(propylene oxide) glycol polymers. The polymers based on poly(tetramethylene oxide) glycol are especially preferred because they are easily prepared, have overall superior physical properties, and are especially resistant to water. I

fhe dicarboxylic acids or their derivatives and the polymeric glycol are incorporated into the final product in the same molar proportions as are present in the reaction mixture. The amount of low molecular weight diol actually incorporated corresponds to the difierence between the moles of diacid and polymeric glycol present in the reaction mixture. When mixtures of low molecular weight diols are employed, the amounts of each diol incorporated isiargely animus of the amounts of diols present, their boiling points, and relative reactivities. The total amount of glycol incorporated is still the difference between moles of diacid and polymeric glycol.

The polymers described herein can be made conveniently by several different methods. Initially, the ester interchange between the dicarboxylic acid ester and the low molecular weight diol and poly(alkylene oxide) glycol must take place. Following this interchange which produces the copolyester product, the polyepoxide is added" to the copolyetherester. The polyepoxide cannot be added prior to the completion of the ester interchange because at the very high temperatures encountered in the final stage of the interchange in the presence of an ester interchange catalyst, the polyepoxide rapidly cross-links the copolyester and raises its melt viscosity to levels which interfere with or prevent operation of the'equipment. Polyepoxides behave under these conditions like polyols andeach epoxide function corresponds to two hydroxyl groups.

The a s awns; 5213656 tbhh' finished copolyester and melt blended with a mix screw for instance while it is still in the molten state and prior to cooling or quenching. Alternatively, the polyepoxide may be added subsequentlyby remelting the finished copolyester. A particularly convenient means of adding solid polyepoxides involves dry blending the polyepoxide with copolyester pellets and passing the dry blend through an extruder or injection molding machine. In this manner melt blending can be combined with extrusion or injection molding forming steps.

iian'sssiyaai si's'tabsasdea man be added with the polyepoxide,but is preferablyadded after the polyepoxide has been at least partially melt blended with the copolyester. The catalyst should not be added to the copolyester in the absence of the polyepoxide as this can cause copolyester degradation. In instances where the epoxide is added to' the molten copolyester emerging from the copolyester process, it is usually desirable not to add catalyst at thispoint. Instead, catalyst can be conveniently mixed with the copolyester as it is being used in operations such as injection molding or extrusion.

In more de taihthe polymers described herein can made conveniently by starting with a conventional ester interchange reaction. A preferred procedure involves heating the dimethyl ester of terephthalic acid with a long-chain glycol and a molar excess of 1,4-butanediol in the presence of a catalyst of l50-260C. while distilling off methanol formed by the ester interchange. Depending on temperature, catalyst, glycol excess, and equipment, this reaction can be completed within a few minutes to a few hours. This procedure results in the preparation of a low molecular weight prepolymer which can be carried to a high molecular weight copolyester of this invention by the procedure described below. Such prepolymers can also be prepared by a number of alternate esterification or ester interchange processes; for example, the longchain glycol can be reacted with a high or low molecular weight short-chain ester homopolymer or copolymer in the presence of catalyst until randomization occurs. The short-chain ester homopolymer or copolymer can be prepared by ester interchange from either the dimethyLester's and low molecular weight diols, as above, or from the free acids with the diol acetates. Alternatively, the short-chain ester copolymer can be prepared by direct esterification from appropriate acids, anhydrides, or acid chlorides, for example, with diols or by other processes such as reaction of the acids with cyclic ethers or carbonates. Obviously, the prepolymer might also be prepared by running these processes in the presence of the longchain glycol.

The resulting prepolymer is then carried to high molecular weight by distillation of the excess of shortchain diol. This process is known as polycondensation.

Additional ester interchange occurs during this polycondensation or distillation; the distillation serves to increase the molecular weight and to randomize the arrangement of the copolyester units. Best results are usually obtained if this final distillation or polycondensation is run at less than 1 mm. Hg pressure and 240260C. for less than 2 hours, e.g., 0.5 to 1.5 hours in the presence of antioxidants such as sym-di-betanaphthyl-p-phenylenediamine and 1,3,5-trimethyl- 2,4,6-tris[ 3 ,5 -ditertiarybutyl-4-hydroxybenzyl] benzene. Most practical polymerization techniques rely upon ester interchange to complete the polymerization reaction. In order to avoid excessive hold time at high temperatures with possible irreversible thermal degradation, a catalyst for the ester interchange reaction should be employed. While a wide variety of catalysts can be used organic titanates such a tetrabutyl titanate used alone or in combination with magnesium or calcium acetates are preferred. Complex titanates, such as Mg[HTi(OR) ]2, derived from alkali or alkaline earth metal alkoxides and titanate esters are also very effective. Inorganic titanates, such as lanthanum titanate, calcium acetate/antimony trioxide mixtures and lithium and magnesium alkoxides are representative of other catalysts which can be used.

Ester interchange polymerizations are generally run in the melt without added solvent, but inert solvents can be used to facilitate removal of volatile components from the mass at low temperatures. This copolyester polymer preparation. Polycondensation of prepolymer can also be accomplished in the solid phase by heating divided solid prepolymer in a vacuum or in a stream of inert gas to remove liberated low molecular weight diol; This method has the advantage of reducing degradation because it must be used at temperatures below the softening point of the prepolymer.

The properties of these copolyetheresters can be modified by incorporation of various conventional inorganic fillers such as carbon black, silica 'gel, alumina, clays, and chopped fiberglass. In general, these additives have the effect of increasing the modulus of the material at various elongations. Compounds having a range of hardness values can be obtained by blending hard and soft polyesters of this invention.

Following the formation of copolyester and while it is i still in the molten state being maintained at a temperature of about to 275C about 0.5-10.0 equivalents preferably 1.0-5.0 equivalents per equivalent of carboxyl group of the polyester, of a polyepoxide having a functionality of not less than about two can be added to the copolyester. It should be noted that at that point the copolyester polymer has a molecular weight corresponding to an inherent viscosity of about 1.0 to 1.5. The polyepoxide can be added by metering it and the molten copolyester into a mix screw after which, the resulting blend should be cooled or quenched. As previously mentioned, the finished copolyester can be quenched and the epoxide can be added at a later time by remelting the copolyester.

The resulting product, that is to say the copolyester polymer modified with the polyepoxide, having a functionality of at least two has the following improved characteristics as compared to the nonmodified polyester polymer. In the absence .of a catalyst the polyepoxide modified copolyesters have improved melt stability so that processing of the molten copolyester can be accomplished at higher temperatures than would normally be acceptable. In the presence of catalysts, the modified copolyester can be chain-extended and/or cross-linked to such an extent that significant improvements in physicalproperties such as tensile and tear strength and flex life are observed. The modified copolyesters, preferably with catalysts, are also useful in preparing hot-melt adhesives because of their outstanding melt stability and the adhesionpromoting character of the polyepoxide.

All parts, proportions and percentages disclosed herein are by weight unless otherwise indicated. The following examples further illustrate the invention:

7 Test Procedures The following ASTM methods are used in determining the properties of the polymers in the examples:

D1484 I D470** D1238 EXAMPLES Copolyester A is prepared by ester interchange of 4.84 moles of, dimethyl terephthalate hereinafter (DMT), 1 .41 moles of dimethyl isophthalate hereinafter (DMI), 1.0 mole of polytetr'amethyleneether glycol hereinafter (PT- MEG-980) (having a number average molecular weight about 980) and excess 1,4-butanedio1in the presence of a tetrabutyl titanate/magnesium acetate catalyst and a stabilizer [sym-di-beta-naphthyl-phenylene diamine]. Ester interchange is conducted at atmospheric pressure up to a final temperature of 220C. The ester interchange is followed by polycondensation at 250C. at less than 1 mm. Hg for about 90 minutes. The resulting polymer has a melt index of 11.4 measured at 250C. which corresponds to an inherent viscosity of about 1.72 and contains about 27.2 milliequivalents of carboxyl groups per kilogram (kg.) of polymer.

Copolyester Bis prepared by ester interchange of: 7.85 moles of DMT, 1 mole PTMEG-980 and excess 1,4-butanediol using the ester interchange conditions and catalyst and stabilizer described for the preparation of Copolyester A. Polycondensation is performed at-250C. for about 5 hours under reduced pressure. At the end of the finishing cycle the pressure was about 5 mm. Hg. The resulting polymer had a melt index of 48.8 measured at 220C. and a carboxyl content of 73.9 milliequivalents/kg.

Copolyester C is prepared from the same molar amounts of DMT, PTMEG-980 and 1,4-butanediol as used for the preparation of CopolyesterB. The ester interchange and polycondensation reaction is effected under the same conditions and in the presence of the same stabilizer and catalyst as described for the preparation of Copolyester A. The resulting polymer had a melt index of 6.7 (measured at 220C.) and carboxyl content of 27.9 milliequivalents/kg.

Polyepoxide A is mixed with Copolyester A in the amounts tabulated below. The compounding is effected by milling on a steam-heated rubber mill at -170 C. for 5 minutes. In experiment 1B the catalyst was polymer for a few minutes.

' 1A 1B 1C 1D Copolyester A (parts) 100 100 100 100 Polyepoxide A (parts) 2.0 1.0 Catalyst A (parts) 0.15 0.3

In control experiment 1D Copolyester A was milled without polyepoxide or catalyst addition to give the polymer the same heat history.

To determine the melt stability of polymer compositions 1A to D under conditions similar to those during processing 7.5 g. samples of shreddedpolymer of each composition were dried at l35C/0.05 mm. Hg. for 1 hour and then charged to a melt index apparatus (available from F. F. Slocomb, Wilmington, Del.) heated at 250C. The change of melt index was then determined as a function of time. The initial melt index was determined 5 minutes after charging-thep'olymer to the meltindexer. The results are summarized below:

Melt index determined after 10 minutds at 250'C.

Equivalent weight.

'lolyepoxlde A Range of equivalent weight for commercially available material approximating the indicated structure.

Since the melt index is inversely proportional'to the melt viscosity a plus change means a decrease of molecular weight due to polymer degradation. It is evident that Composition 1A containing Polyepoxide A exhibits significantly better melt stability under these conditions than Control polymer .1 D. In the presence of amine catalyst the polyepoxide is even more effective and the molecular weight of the copolyester actually increased slightly as indicated by the negative. change of I melt'index (Composition 1B). This is surprising in view of the fact that the amine catalyst alone has a very detrimental effect on the melt stability of the polymer (Composition 1C).

Example 2 About 1.0 part of Polyepoxide A and 0.2 part of amine Catalyst A are mixed with 50 parts of Copolyester B in an agitated flask at 230C under a nitrogen atmosphere. The preferred procedure consists 20 of melting first the copolyester followed by the addition ofthe polyepoxide and finally the amine catalyst. The liquid mixture is agitated slowly for 18 minutes under these conditions. Properties are measured on slabs of.

80 mil thickness whichare prepared by compression 5 molding at about 240C and aftercuring at 100C for 16 hours. Properties of the original copolyester and that mixed with the polyepoxide are tabulated below:

Copolyester lus Original p Copolyester Polyepoxide A, 7

Melt index 220C,g/l0 min. 48.8 Y 0.4 1 COOH end group conc., 73.9 nil s/ s Tensile strength psi 3000 5100 Elongation at'break, 460 700 100% Modulus, psi 2250 2360 300% Modulus, psi 2300 2410 Trouser tear, pli 260 430 Shore D hardness 55 55 Substantial increases in tensile strength, and tear 40 strengthare obtained as a result of the polyepoxide modification.

. Above example was essentially repeated except that 0.5 part of Polyepoxide C was used instead of 1.0 part of Polyepoxide A. After mixing for 18 minutes at' 230C. the melt index measured at 220C. was reduced from 48.8 to 13.4g/l0 min. Aftercure for 16 hours at 100C did not result in a lower melt index indicating that the reaction was essentially completed under the conditions employed. A similar improvement of physi- 5 cal properties was obtained as observed above.

Example 3 One'partof Polyepoxide C is mixed with 100 parts of dried Copolyester C in an agitated flask at 250C. for 15 minutes under a nitrogen atmosphere. The resulting polymer blend is then shredded and dried at 130C/10 mm. Hg. for 2 hours and processed by injection molding on 'a l-oz. ram-type machine (Imperial Injection Molder, Newbury Industries, Model H 1-30T) under the following conditions:

Cylinder temperature (all zones) 275C. Ram Pressure 7000 psi Cycle time 2 min. Average residence time/cycle 9.5 min.

Mold temperature The above injection molded parts are. then recycled immediately after demolding. The conditions. were selected to simulate the injection molding of large parts in commercial equipment.

Carboxyl content, milliequivalents/kg.

Original olymer After 2 cgcles The significantly improved melt stability of the polyepoxide modified copolyester is evident from the melt index data and the carboxyl content values. The higher molecular weight (lower melt index.) of the polyepoxide containing polymer after injectionmolding results in. improved physical properties suchas-tensile and tear strength as well as, flex life. The lower carboxyl content manifests *itself in improved aging characteristics of the polymer, especially in respect to hydrolytic stability.

Example 4 Polyepoxide C is compounded with Copolyester A as described in Example 1, in the amounts tabulated. below:

4A 4B Copolyester A (parts) 100 100 Polyepoxide C (parts) 1.0 2.0 Catalyst A (parts) 0.2 0.3

After shredding and drying of the compounded polymers, mil slabs were compression molded at 240C and cured for 20 hours at C. The cured polymer was no longer thermoplastic anddid not melt at 250C. Properties of the original copolyester and. those modified withpolyepoxide are tabulated below; v

- Polye xide I Mod led Original Copolyester Copoly- Y ester 4A 4B Tensile strength, psi 4600 5050 5000 Elongation atbreak, 800 720 690 100% Modulus, psi 850 1120. 1 210 100% Modulus, psi 1100 1540 1825 500% Modulus, psi '1700 2410 3000 Trouser, tear, pli 240 228 Hardness, Shore A 91 90 92' The epoxide modification followed by curing resulted in a thermosetting. polymer composition with the processing characteristics of a thermoplastic. Furthermore, substantial. improvements in the moduli charac teristics were obtained without increase in hardness.

What is claimed is:

l. A segmented. thermoplastic copolyestercomposb tion consisting essentially of (a) a multiplicity of recurring long chain ester units and short chain ester units joined head-to-tail through ester linkages, said long chain ester units being represented by the formula andsaid shortchain units being represented by the formula where G is a divalent radical remaining after the removal of terminal hydroxyl groups from a poly(alkylene-oxide) glycol having a molecular weight of about 400-6,000 and a carbon to oxygen ratio of about 2.0-4.3; R' is a divalent radical remaining after removal of carboxyl groups from a dicarboxylic acid having a molecular weight less than about 300 and D is a divalent radical remaining after removal of hydroxyl groups from a diol having a molecular weight less than about 250; provided said short chain ester units amount to about-15995 percent by weight of saidcopolyester,

wherein n has a value of about 2 to R, R' and having a functionality of esters and mixtures thereof.

R"" are independently selected from the'group con sisting of hydrogen and lower alkyl, R" is a polyvalent radical consisting essentially of C, Hand 0, and R" and R" may be joined to form a carboxylic ring.

4. The composition of claim 3 wherein R contains 7 carbocyclic aromatic nuclei substituted with Cl or Br.

5. The composition of claim 3 wherein R' and'Rrf' are hydrogen, n is 2 to 10 and the polyepoxide has an epoxide equivalent of about ,000. i I

' 6. The composition of claim 3- wherein said polyepoxide is a polyglycidyl compound.

7.' The composition of claim 1 wherein said polyepoxide is a diglycidyl ether of bis'phenol A.

8. The composition of claim 1 wherein said copolyester also contains 0.05- 0.5 weight percent, based on the weight of copolyester, of an epoxy catalyst.

9. The composition of claim 8 wherein said epoxy catalyst is a secondary aliphatic amine.

10. The composition of claim-9 wherein said secondary amine has a boiling point at least about as high as the meltingpoint of said copoiyester.

'11. The composition of claim 1 wherein said dicarboxylic acidis selectedfrom the group consisting 'of phthalic acid, terephthalic acid,'isop'hthalic acid, their 12. The composition of claim 1 wherein the poly(alkylene oxide) glycol is poly(tetramethylene oxide) glycol having a molecular weight of about'600-2,000.

13. The composition of claim 1 wherein said diol is l,4-butanediol. Y i 14. The composition .of claim 1 v wherein said polyepoxideis a polyglycidyl ether of a phenol-formaldehyde novolac.

15. The composition of claim 9 wherein' said glycol is poly(tetramethylene oxide) glycol having a'molecular weight of about 600-2,000, said .dicarboxylic acid is dimethyl terephthalate and said diol is l ,4-butanediol.

16..The composition of claim'9 wherein said dicarboxylic acid is a mixture of dimethyl terephthalate and a maximum of 30 mole percent of dimethyl isophthalate, dimethyl phthalate or mixtures thereof. 

2. The composition of claim 1 wherein a maximum of 100 milliequivalents of carboxyl groups are present per kilogram of polymer.
 3. The composition of claim 1 wherein the polyepoxide has an epoxide equivalent of about 50-2,000 and is represented by the general formula:
 4. The composition of claim 3 wherein R'''' contains carbocyclic aromatic nuclei substituted with Cl or Br.
 5. The composition of claim 3 wherein R'''''' and R'''''''' are hydrogen, n is 2 to 10 and the polyepoxide has an epoxide equivalent of about 75-1,000.
 6. The composition of claim 3 wherein said polyepoxide is a polyglycidyl compound.
 7. The composition of claim 1 wherein said polyepoxide is a diglycidyl ether of bisphenol A.
 8. The composition of claim 1 wherein said copolyester also contains 0.05-0.5 weight percent, based on the weight of copolyester, of an epoxy catalyst.
 9. The composition of claim 8 wherein said epoxy catalyst is a secondary aliphatic amine.
 10. The composition of claim 9 wherein said secondary amine has a boiling point at least about as high as the melting point of said copolyester.
 11. The composition of claim 1 wherein said dicarboxylic acid is selected from the group consisting of phthalic acid, terephthalic acid, isophthalic acid, their esters and mixtures thereof.
 12. The composition of claim 1 wherein the poly(alkylene oxide) glycol is poly(tetramethylene oxide) glycol having a molecular weight of about 600-2,000.
 13. The composition of claim 1 wherein said diol is 1,4-butanediol.
 14. The composition of claim 1 wherein said polyepoxide is a polyglycidyl ether of a phenol-formaldehyde novolac.
 15. The composition of claim 9 wherein said glycol is poly(tetramethylene oxide) glycol having a molecular weight of about 600-2,000, said dicarboxylic acid is dimethyl terephthalate and said diol is 1,4-butanediol.
 16. The composition of claim 9 wherein said dicarboxylic acid is a mixture of dimethyl terephthalate and a maximum of 30 mole percent of dimethyl isophthalate, dimethyl phthalate or mixtures thereof. 